What does `app.use(bodyParser.json())` do?

Okay, contrary to what I previously thought, further research shows that extended: true and app.use(bodyParser.json()) can be used together. So it is not only extended: false that uses it. The statement app.use(bodyParser.json()) is to be used independently, whether you set extended as true or false.

• app.use(bodyParser.json()) basically tells the system that you want json to be used.

• bodyParser.urlencoded({extended: ...}) basically tells the system whether you want to use a simple algorithm for shallow parsing (i.e. false) or complex algorithm for deep parsing that can deal with nested objects (i.e. true).

Have a look at the docs (i.e. https://expressjs.com/en/guide/migrating-4.html) for the example.

URL encoding and JSON encoding both allow to convert a (nested) object to string, but the format is different. An URL encoded string is in general not a valid JSON string.

One application may use one encoding method, and another the other. As long as they don't mix the two, it will work.

bodyParser.json returns middleware that only parses json. This parser accepts any Unicode encoding of the body and supports automatic inflation of gzip and deflate encodings.

A new body object containing the parsed data is populated on the request object after the middleware (i.e. req.body).